Mild and Selective Vanadium-Catalyzed Oxidation of Benzylic, Allylic, and Propargylic Alcohols Using Air

ABSTRACT

The invention concerns processes for oxidizing an alcohol to produce a carbonyl compound. The processes comprise contacting the alcohol with (i) a gaseous mixture comprising oxygen; and (ii) an amine compound in the presence of a catalyst, having the formula: 
     
       
         
         
             
             
         
       
     
     where each of R 1 -R 12  are independently H, alkyl, aryl, CF 3 , halogen, OR 13 , SO 3 R 14 , C(O)R 15 , CONR 16 R 17  or CO 2 R 18 ; each of R 13 -R 18  is independently alkyl or aryl; and Z is alkl or aryl.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/450,502 entitled “Mild and SelectiveVanadium-Catalyzed Oxidation of Benzylic, Allylic, and PropargylicAlcohols Using Air,” filed Mar. 8, 2011, and is incorporated herein inits entirety by reference.

STATEMENT REGARDING FEDERAL RIGHTS

This invention was made with government support under Contract No.DE-AC52-06NA25396 awarded by the U.S. Department of Energy. Thegovernment has certain rights in the invention.

TECHNICAL FIELD

The present invention relates to the oxidation of alcohols in thepresence of vanadium-containing catalyst.

BACKGROUND

The oxidation of alcohols to afford carbonyl compounds is a key reactionin synthetic organic chemistry. Recent years have seen major progress inthe development of catalytic aerobic alcohol oxidation, which offerseconomic and environmental benefits over traditional stoichiometricoxidants (Schultz, M. J.; Sigman, M. S. Tetrahedron 2006, 62, 8227-8241;Punniyamurthy, T.; Velusamy, S.; Iqbal, J. Chem. Rev. 2005, 105,2329-2363; Stahl, S. S. Angew. Chem. Int. Ed. 2004, 43, 3400-3420).Despite these advances, many reported catalysts include precious metals(Pd, Ru, Ir) and use oxygen pressures of 1 atm or more (Schultz, M. J.;Adler, R. S.; Zierkiewicz, W.; Privalov, T.; Sigman, M. S. J. Am. Chem.Soc. 2005, 127, 8499-8507; Steinhoff, B. A.; Guzei, I. A.; Stahl, S. S.J. Am. Chem. Soc. 2004, 126, 11268-11278; ten Brink, G. J.; Arends, I.W. C. E.; Sheldon, R. A. Science 2000, 287, 1636-1639; Nishimura, T.;Onoue, T.; Ohe, K.; Uemura, S. J. Org. Chem. 1999, 64, 6750-6755;Johnston, E. V.; Karlsson, E. A.; Tran, L. H.; Akermark, B.; Backvall,J. E. Eur. J. Org. Chem. 2010, 1971-1976; Nikaidou, F.; Ushiyama, H.;Yamaguchi, K.; Yamashita, K.; Mizuno, N. J. Phys. Chem. C 2010, 114,10873-10880; Mizoguchi, H.; Uchida, T.; Ishida, K.; Katsuki, T.Tetrahedron Lett. 2009, 50, 3432-3435; Wolfson, A.; Wuyts, S.; De Vos,D. E.; Vankelecom, I. F. J.; Jacobs, P. A. Tetrahedron Lett. 2002, 43,8107-8110; Arita, S.; Koike, T.; Kayaki, Y.; Ikariya, T. Angew. Chem.Int. Ed. 2008, 47, 2447-2449; Jiang, B.; Feng, Y.; Ison, E. A. J. Am.Chem. Soc. 2008, 130, 14462-14464; Gabrielsson, A.; van Leeuwen, P.;Kaim, W. Chem. Commun. 2006, 4926-4927). There is considerable interestin replacing precious metal-containing catalysts with basemetal-containing catalysts because base metals are less expensive andmore abundant that precious metals (Michel, C.; Belanzoni, P.; Gamez,P.; Reedijk, J.; Baerends, E. J. Inorg. Chem. 2009, 48, 11909-11920;Jiang, N.; Ragauskas, A. J. J. Org. Chem. 2006, 71, 7087-7090; Gamez,P.; Arends, I. W. C. E.; Sheldon, R. A.; Reedijk, J. Adv. Synth. Catal.2004, 346, 805-811; Gamez, P.; Arends, I. W. C. E.; Reedijk, J.;Sheldon, R. A. Chem. Commun. 2003, 2414-2415; Chaudhuri, P.; Hess, M.;Florke, U.; Wieghardt, K. Angew. Chem. Int. Ed. 1998, 37, 2217-2220;Marko, I. E.; Giles, P. R.; Tsukazaki, M.; Brown, S. M.; Urch, C. J.Science 1996, 274, 2044-2046). Using air instead of pure oxygen (O₂) isalso advantageous (for selected examples of aerobic oxidation using airsee: (a) Zahmakiran, M.; Akbayrak, S.; Kodaira, T.; Ozkar, S. DaltonTrans. 2010, 39, 7521-7527; Bailie, D. S.; Clendenning, G. M. A.;McNamee, L.; Muldoon, M. J. Chem. Commun. 2010, 46, 7238-7240; Conley,N. R.; Labios, L. A.; Pearson, D. M.; McCrory, C. C. L.; Waymouth, R. M.Organometallics 2007, 26, 5447-5453; Guan, B.; Xing, D.; Cai, G.; Wan,X.; Yu, N.; Fang, Z.; Yang, L.; Shi, Z. J. Am. Chem. Soc. 2005, 127,18004-18005; Iwasawa, T.; Tokunaga, M.; Obora, Y.; Tsuji, Y. J. Am.Chem. Soc. 2004, 126, 6554-6555; Korovchenko, P.; Donze, C.; Gallezot,P.; Besson, M. Catal. Today 2007, 121, 13-21; Hara, T.; Ishikawa, M.;Sawada, J.; Ichikuni, N.; Shimazu, S. Green Chem. 2009, 11, 2034-2040),reducing the safety hazard associated with heating organic solventsunder elevated O₂ pressures.

Vanadium complexes have shown potential as base-metal catalysts foraerobic alcohol oxidation, in some cases proving effective forsubstrates where palladium catalysts display limited activity. Forinstance, vanadium is known to catalyze the selective aerobic oxidationof propargylic alcohols, a reaction using V^(IV)(O)(acac)₂ (1-5 mol %)and molecular sieves at 80° C. (Maeda, Y.; Kakiuchi, N.; Matsumura, S.;Nishimura, T.; Kawamura, T.; Uemura, S. J. Org. Chem. 2002, 67,6718-6724; Maeda, Y.; Kakiuchi, N.; Matsumura, S.; Nishimura, T.;Uemura, S. Tetrahedron Lett. 2001, 42, 8877-8879). The combination ofV^(IV)(O)(acac)₂ and DABCO (DABCO=1,4-diazabicyclo[2.2.2]octane) alsocatalyzes the oxidation of benzylic and allylic alcohols in ionic liquidsolvent at 80-100° C. (Jiang, N.; Ragauskas, A. J. Tetrahedron Lett.2007, 48, 273-276; Jiang, N.; Ragauskas, A. J. J. Org. Chem. 2007, 72,7030-7033). Vanadium catalysts with chiral Schiff-base ligands effectthe oxidative kinetic resolution of α-hydroxyesters, amides, andphosphonates (Radosevich, A. T.; Musich, C.; Toste, F. D. J. Am. Chem.Soc. 2005, 127, 1090-1091; Pawar, V. D.; Bettigeri, S.; Weng, S. S.;Kao, J. Q.; Chen, C. T. J. Am. Chem. Soc. 2006, 128, 6308-6309; Weng, S.S.; Shen, M. W.; Kao, J. Q.; Munot, Y. S.; Chen, C. T. Proc. Nat. Acad.Sci. 2006, 103, 3522-3527). These reports are promising indications ofthe versatility of vanadium catalysts, but each requires an atmosphereof pure oxygen. Very recently, Ohde and Limberg reported ametavanadate-cinnamic acid catalyst that catalyzes the oxidation ofactivated alcohols using mixtures of argon and O₂, but this catalyst ishighly moisture sensitive (Ohde, C.; Limberg, C. Chem. Eur. J. 2010, 16,6892-6899).

There is a need in the art for an oxidation process that utilizes arobust base metal catalyst which can oxidize alcohols in the presence ofair.

SUMMARY

The present invention provides processes for oxidizing an alcohol toproduce a carbonyl compound, the process comprising contacting thealcohol with

(i) a gaseous mixture comprising oxygen; and

(ii) an amine compound;

the contacting occurring in the presence of a catalyst comprising twonitrogen-containing heterocycles complexed with vanadium and having theformula:

where each of R¹-R¹² are independently H, alkyl, aryl, CF₃, halogen,OR¹³, SO₃R¹⁴, C(O)R¹⁵, CONR¹⁶R¹⁷ or CO₂R¹⁸; each of R¹³-R¹⁸ isindependently alkyl or aryl; and Z is alkl or aryl. In some embodiments,the contacting is performed in a gaseous mixture comprising from 5 toabout 35 molar percent oxygen.

In some embodiments, Z is alkyl. In one preferred embodiment, Z isisopropyl. Some amines useful in the inventive reaction are trialkylamines. Preferred amines include triethylamine, diisopropylethylamine,1,4-diazabicyclo[2.2.2]octane, or 2,2,6,6-tetramethylpiperidine-1-oxyl.One preferred amine is triethylamine.

Some catalysts are of a formula where each of R¹-R¹² is H, alkyl oraryl. In one preferred embodiment, each of R¹-R¹² is H.

While the invention is applicable to numerous alcohols, some preferredalcohols are of the formula:

where R¹⁹ is selected from aryl, vinyl, and alkynyl, and R²⁰ is selectedfrom H, methyl, and aryl. In some preferred embodiments, the alcohol isa benzylic alcohol, allylic alcohol, or propargylic alcohol.

The process of the invention may be run with or without the presence ofa solvent. In some preferred embodiments, the contacting of thereactants and catalyst occurs in the presence of a solvent selected fromone or more of water, 1,2-dichloroethane, ethylacetate, toluene,tetrahydrofuran, acetonitrile, dichloromethane, 1,2-dichlorobenzene and2-methyl-tetrahydrofuran.

In some embodiments, the contacting occurs at a temperature in the rangeof from ambient temperature (e.g., 25° C. to 150° C.). In otherembodiments, the temperature is in the range of from 40° C. to 80° C. or40° C. to 75° C. or 50° C. to 70° C. In certain embodiments, the gaseousmixture is air. In other embodiments, the gaseous mixture is a mixtureof inert gas (such as nitrogen or argon) and oxygen.

In one preferred embodiment, the catalyst is of the formula

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of an oxidation reaction.

FIG. 2 (Scheme 1) shows results for the oxidation of4-methoxybenzylalcohol with a variety of catalysts.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention is concerned with a vanadium-based catalyst forthe aerobic oxidation of benzylic, allylic, and propargylic alcohols.See, for example, FIG. 1. The oxidation reactions proceed under mildconditions (air, 40-80° C.), and in a variety of solvents. Moreover, thecatalyst can be prepared in air using commercially available reagents,making the overall process inexpensive, simple, and accessible withoutrequiring the use of a drybox or Schlenk techniques.

We recently studied the mechanism of alcohol oxidation by dipicolinatevanadium(V) complexes, and found that the base known as pyridinepromoted alcohol oxidation (Hanson, S. K.; Baker, R. T.; Gordon, J. C.;Scott, B. L.; Silks, L. A.; Thorn, D. L. J. Am. Chem. Soc. 2010, 132,17804-17816). Inspired by this finding, we tested the aerobic oxidationof 4-methoxybenzyl alcohol at 60° C. under air using several differentvanadium complexes (2 mol %) and a base promoter (10 mol % NEt₃) in1,2-dichloroethane (Scheme 1, FIG. 2). Poor yields were observed withV^(IV)(O)(acac)₂, V^(V)(O)(O^(i)Pr)₃, and complexes of carboxylate-basedligands (dipicolinate (3) and 8-quinolinate-2-carboxylate (4)).Complexes with more electron-donating ligands displayed higher activity(Thorn, D. L.; Harlow, R. L.; Herron, N. Inorg. Chem. 1996, 35, 547-548;Nica, S.; Pohlmann, A.; Plass, W. Eur. J. Inorg. Chem. 2005, 2032-2036;Caravan, P.; Gelmini, L.; Glover, N.; Herring, F. G.; Li, H.; McNeill,J. H.; Rettig, S. J.; Setyawati, I. A.; Shuter, E.; Sun, Y.; Tracey, A.S.; Yuen, V. G.; Orvig, C. J. Am. Chem. Soc. 1995, 117, 12759-12770;Sun, Y.; James, B. R.; Rettig, S. J.; Orvig, C. Inorg. Chem. 1996, 35,1667-1673), with the highest activity observed for the complex(HQ)₂V^(V)(O)(O^(i)Pr) (8) (HQ=8-quinolinate) reported by Sawyer,Floriani, and Scheidt (Scheme 1) (Scheidt, W. R. Inorg. Chem. 1973, 12,1758-1761; Giacomelli, A.; Floriani, C.; Duarte, A. O. D. S.;Chiesi-Villa, A.; Guastini, C. Inorg. Chem. 1982, 21, 3310-3316; (b)Pasquali, M.; Landi, A.; Floriani, C. Inorg. Chem. 1979, 18, 2397-2400.;Riechel, T. L.; Sawyer, D. T. Inorg. Chem. 1975, 14, 1869-1875; (b)Amos, L. W.; Sawyer, D. T. Inorg. Chem. 1974, 13, 78-83). Complex 8 iseasily prepared in one step by the reaction of 8-hydroxyquinoline withV^(IV)(O)(acac)₂ under air in isopropanol (see the examples below).

TABLE 1 Solvents tested for the oxidation of 4-methoxybenzylalcoholEntry Solvent % yield (NMR) 1 1,2-dichloroethane 99 2 Ethyl acetate 91(99) 3 toluene 78 (96) 4 Tetrahydrofuran (THF) 96 (99) 5 Acetonitrile(CH₃CN) 93 (98) 6 Dichloromethane (CH₂Cl₂) 92^(a) (99^(a)) 71,2-dichlorobenzene 99 8 2-methyl-THF 99 9 Dimethylsulfoxide (DMSO) 6910  pyridine 12 Conditions: 2 mol % 8, 10 mol % triethylamine (NEt3), 60C., 24 hours. Conditions for dichloromethane: 5 mol % 8, 40 C. Values inparenthesis indicate percent yield after 48 hours reaction time.

Use of several different solvents for the oxidation of4-methoxybenzylalcohol using 8 (2 mol %) and NEt₃ (10 mol %) werescreened. High yields of the aldehyde were observed after 24 h at 60° C.in THF, ethyl acetate, and acetonitrile, with >99% NMR yield observed in1,2-dichloroethane, 1,2-dichlorobenzene, and 2-methyltetrahydrofuran(Table 1, Entries 1 to 8).

The effect of the additive was then examined for the oxidation of4-methoxybenzylalcohol using 8 (2 mol %) in 1,2-dichloroethane (Table2). Triethylamine, diisopropylethylamine, and TEMPO were all effectivepromoters of the vanadium complex, affording high yields of4-methoxybenzaldehyde after 24 h at 60° C. (Entries 2 to 5). Incontrast, less than 5% yield was observed with the vanadium complexalone (no additive, Entry 1), suggesting a key role for the nitrogenbase.

TABLE 2 additives tested for the oxidation of 4-methoxybenzyl alcoholentry additive % yield (NMR)  1 none  4  2 triethylamine 99 (49)  3Triethylamine (5 mol %) 99 (42)  4 diisopropylethylamine 99 (31)  5TEMPO 99 (8)  6 DABCO 83  7 DMAP 28  8 NaO^(t)Bu 19  9 Na₂CO₃ 16 10 DBU 5 11 Proton sponge  6 12 NaOAc  1 Conditions: 2 mol % 8, 10 mol %additive, 1,2-dichloroethane solvent, 60° C., 24 hours. Values inparenthesis indicate yields after 4 hours.

The substrate scope of the alcohol oxidation was investigated, using 8(2 mol %) and NEt₃ (10 mol %) in 1,2-dichloroethane (Table 3). A rangeof benzylic alcohols were oxidized and the aldehydes or ketones isolatedin high yields (Entries 1 to 8). Steric bulk around the alcohol slowedthe reaction, with the more hindered α-isopropyl- and α-tert-butylbenzyl alcohols showing only 20 and 0% yield, respectively (Entries 7and 8). Cinnamyl alcohol, 3-methyl-2-cyclohexen-1-ol,5-hydroxy-methylfurfural (HMF), and 2-hydroxymethylpyridine wereoxidized to the corresponding aldehyde or ketone in high yields (Entries9 to 12).

2-Allyloxybenzylalcohol has been used by Galli and coworkers as asubstrate probe in catalytic oxidations to detect the intermediateformation of a carbon-based radical, which has been reported to undergoan intramolecular ring closure as shown in Scheme 2 (Astolfi, P.;Brandi, P.; Galli, C.; Gentili, P.; Gerini, M. F.; Greci, L.;Lanzalunga, O, New J. Chem. 2005, 29, 1308-1317; Minisci, F.; Recupero,F.; Cecchetto, A.; Gambarotti, C.; Punta, C.; Faletti, R.; Paganelli,R.; Pedulli, G. F. Eur. J. Org. Chem. 2004, 109-119; and Bentley, J.;Nilsson, P. A.; Parsons, A. F. J. Chem. Soc., Perkin Trans 1, 2002,1461-1469). This substrate was oxidized to the corresponding aldehyde in95% isolated yield (Entry 13); none of ring-closed product A (Scheme 2)was detected by ¹H NMR (Astolfi, P.; Brandi, P.; Galli, C.; Gentili, P.;Gerini, M. F.; Greci, L.; Lanzalunga, O, New J. Chem. 2005, 29,1308-1317; and Minisci, F.; Recupero, F.; Cecchetto, A.; Gambarotti, C.;Punta, C.; Faletti, R.; Paganelli, R.; Pedulli, G. F. Eur. J. Org. Chem.2004, 109-119).

The secondary propargylic alcohol 4-phenyl-3-butyn-2-ol was alsooxidized in high yield (96%, Entry 14). Primary propargylic alcohols3-phenyl-2-propyn-1-ol and 2-decyn-1-ol were oxidized to thecorresponding aldehydes in good yields (80% and 60% ¹H NMR yields,Entries 15 and 16, respectively). Oxidation of the terminal alkyne1-phenyl-2-propyn-1-ol was less selective, affording the ketone productin only 38% yield (¹H NMR, Entry 17) at complete conversion.

Simple aliphatic alcohols such as 1-butanol and 2-butanol underwentlittle or no oxidation, even when heated at 100° C. (Entries 18 and 19).This observed selectivity for activated alcohols was confirmed byoxidation of a mixture of 4-methoxybenzylic alcohol (5 mmol) and1-octanol (5 mmol), which resulted in complete oxidation of the benzylicalcohol with no formation of 1-octanal.

For several of the benzylic alcohols, the oxidation proceededselectively with no solvent (neat) using 8 (2 mol %) and NEt₃ (10 mol %)for 24 h at 100° C. However, lower selectivities were observed for theoxidations of cinnamyl alcohol, 5-hydroxymethylfurfural, and4-phenyl-3-butyn-2-ol when no solvent was used.

To gain insight into the role of the base additive,(HQ)₂V^(V)(O)(OC₆H₄OCH₃) (9) was prepared from the reaction of 8 with4-methoxybenzylalcohol in acetonitrile. In the absence of base, complex9 was relatively stable in CD₂Cl₂ solution, with less than 5% reactingafter 16 h at room temperature. However, a rapid reaction occurred whena CD₂Cl₂ solution of 9 was treated with NEt₃ (2 equiv) under argon,affording the vanadium(IV) complex (HQ)₂V^(IV)(O) (10),4-methoxy-benzaldehyde (0.5 equiv, 100% yield) and4-methoxybenzylalcohol (0.5 equiv, 100% yield) within 2 h at roomtemperature (Scheme 3). The increased reactivity observed in thepresence of NEt₃ suggests a key role for the base additive in promotingthe alcohol oxidation step. When the reaction of 9 with NEt₃ was carriedout under air in CD₂Cl₂, quantitative conversion to the cis-dioxovanadium(V) complex (HQ)₂V^(V)(O)₂HNEt₃ (11) and 4-methoxybenzaldehydewas observed after 22 h at room temperature. Complex 11 wasindependently prepared by the reaction of the μ-oxo complex[(HQ)₂V^(V)(O)]₂μ-O (12) (Giacomelli, A.; Floriani, C.; Duarte, A. O. D.S.; Chiesi-Villa, A.; Guastini, C. Inorg. Chem. 1982, 21, 3310-3316)with H₂O and NEt₃ in CH₂Cl₂. When tested for the oxidation of4-methoxybenzylalcohol in combination with 10 mol % NEt₃, both complexes10 and 11 were effective catalysts, affording complete conversion in 24h at 60° C.

TABLE 3 Catalytic oxidation results. en- % try substrate product yield 1  2  3  4  5  6  7  8

  92   96   96   93^(d)   95^(a,f)   90^(a,c) (20)^(a,d)    0^(a,d)  9

  98 10

  96^(a) 11

  98^(a) 12

  94 13

  95 14

  96^(a) 15

(80) 16

(60) 17

(38) 18

 (5)^(b) 19

 (1)^(b) Conditions: 2 mol % 8, 10 mol % NEt₃, 1,2-dichloroethanesolvents, 60° C., 24 h. ^(a)80° C.; ^(b)100° C., dichlorobenzenesolvent; ^(c)48 h; ^(d)72 h; ^(f)= 1 equivalent NEt₃. Values inparenthesis indicate NMR yield.

Initial experiments suggest that mass transport of oxygen may be arate-limiting factor in the oxidation of 4-methoxybenzyl alcohol(Steinhoff, B. A.; Stahl, S. S. J. Am. Chem. Soc. 2006, 128, 4348-4355).When the oxidation was carried out in two different reaction vesselsunder otherwise identical conditions and stopped at an intermediatereaction time (4 h) (Conditions: 2 mol % 8, 10 mol % NEt₃,1,2-dichloroethane solvent, 60° C.), the shape of the reaction vesselaffected the extent of conversion. In a wide 100 mL round bottom flask,55% conversion was observed after 4 h, while in a narrow 10 mL reactiontube, only 31% conversion occurred. The stir rate also affected theextent of conversion in two identical reactions conducted in 25 mL roundbottom flasks.

In 1,2-dichloroethane, the catalytic oxidation of4-methoxy-benzylalcohol was not found to be significantly affected byadded water. When excess water (5 equiv, 5 mmol) was added to theoxidation of 4-methoxybenzylalcohol (1 mmol), >98% conversion to thealdehyde was observed after 24 h at 60° C. This tolerance of waterallows the catalytic reaction to be carried out in the absence of dryingagent, in contrast to several other reported vanadium catalysts whichrequire the addition of molecular sieves (Maeda, Y.; Kakiuchi, N.;Matsumura, S.; Nishimura, T.; Kawamura, T.; Uemura, S. J. Org. Chem.2002, 67, 6718-6724; Maeda, Y.; Kakiuchi, N.; Matsumura, S.; Nishimura,T.; Uemura, S. Tetrahedron Lett. 2001, 42, 8877-8879; and Ohde, C.;Limberg, C. Chem. Eur. J. 2010, 16, 6892-6899).

DEFINITIONS

As used herein, the term “alkyl” includes both branched andstraight-chain saturated aliphatic hydrocarbon groups having thespecified number of carbon atoms, e.g. methyl (Me), ethyl (Et), propyl(Pr), isopropyl (i-Pr), isobutyl (i-Bu), secbutyl (s-Bu), tertbutyl(t-Bu), isopentyl, isohexyl and the like. The term “alkyl” furtherincludes both unsubstituted and mono-, di- and tri-substitutedhydrocarbon groups, with halogen substitution particularly preferred insome preferred embodiments. In certain embodiments, preferred alkylgroups have 1 to 6 carbon atoms. In some preferred embodiments, alkylgroups have 1 to 4 carbon atoms. In yet other preferred embodiments,alkyl groups have 1 to 3 carbon atoms.

The term “aryl” means an aromatic carbocyclic moiety of up to 20 carbonatoms (e.g., 5-20), which may be a single ring (monocyclic) or multiplerings (bicyclic, up to three rings) fused together or linked covalently.Any suitable ring position of the aryl moiety may be covalently linkedto the defined chemical structure. Some preferred aryl groups have 5 to20 carbon atoms. Examples of aryl moieties include, but are not limitedto, chemical groups such as phenyl, 1-naphthyl, 2-naphthyl,dihydronaphthyl, tetrahydronaphthyl, biphenyl. anthryl, phenanthryl,fluorenyl, indanyl, biphenylenyl, acenaphthenyl, acenaphthylenyl, andthe like.

The term “halo” includes fluoro, chloro, iodo, and bromo.

The term “amine” includes aliphatic and aromatic amines. Amines includetrialkyl amines, triaryl amines and amines containing both alkyl andaryl groups. Some preferred amines include triethylamine,diisopropylethylamine, 1,4-diazabicyclo[2.2.2]octane, and2,2,6,6-tetramethylpiperidine-1-oxyl.

“Alcohol compound” refers to a compound that includes at least onealcohol group. Some preferred alcohols include benzylic alcohol, allylicalcohol, and propargylic alcohol. Other preferred alcohol compoundsinclude lignin and lignocellulose, two biomass compositions that can beused, for among other things, to produce fuel products.

“Carbonyl compound” refers to a compound that includes at least onecarbonyl group. Some preferred carbonyl compounds are the oxidationproducts of alcohol compounds discussed in the previous paragraph.

Articles indicating inclusion of “Teflon” refer to DuPont's trademarkedfluoropolymer product. Other fluoropolymers may be used in connectionwith the inventive process.

REFERENCES

-   The following references are incorporated by reference herein.-   Schultz, M. J.; Sigman, M. S. Tetrahedron 2006, 62, 8227-8241;-   Punniyamurthy, T.; Velusamy, S.; Iqbal, J. Chem. Rev. 2005, 105,    2329-2363; (c) Stahl,-   S. S. Angew. Chem. Int. Ed. 2004, 43, 3400-3420;-   Schultz, M. J.; Adler, R. S.; Zierkiewicz, W.; Privalov, T.;    Sigman, M. S. J. Am. Chem. Soc. 2005, 127, 8499-8507;-   Steinhoff, B. A.; Guzei, I. A.; Stahl, S. S. J. Am. Chem. Soc. 2004,    126, 11268-11278;-   ten Brink, G. J.; Arends, I. W. C. E.; Sheldon, R. A. Science 2000,    287, 1636-1639;-   Nishimura, T.; Onoue, T.; Ohe, K.; Uemura, S. J. Org. Chem. 1999,    64, 6750-6755;-   Johnston, E. V.; Karlsson, E. A.; Tran, L. H.; Akermark, B.;    Backvall, J. E. Eur. J. Org. Chem. 2010, 1971-1976;-   Nikaidou, F.; Ushiyama, H.; Yamaguchi, K.; Yamashita, K.;    Mizuno, N. J. Phys. Chem. C 2010, 114, 10873-10880;-   Mizoguchi, H.; Uchida, T.; Ishida, K.; Katsuki, T. Tetrahedron Lett.    2009, 50, 3432-3435;-   Wolfson, A.; Wuyts, S.; De Vos, D. E.; Vankelecom, I. F. J.;    Jacobs, P. A. Tetrahedron Lett. 2002, 43, 8107-8110;-   Arita, S.; Koike, T.; Kayaki, Y.; Ikariya, T. Angew. Chem. Int. Ed.    2008, 47, 2447-2449;-   Jiang, B.; Feng, Y.; Ison, E. A. J. Am. Chem. Soc. 2008, 130,    14462-14464;-   Gabrielsson, A.; van Leeuwen, P.; Kaim, W. Chem. Commun. 2006,    4926-4927;-   Michel, C.; Belanzoni, P.; Gamez, P.; Reedijk, J.; Baerends, E. J.    Inorg. Chem. 2009, 48, 11909-11920;-   Jiang, N.; Ragauskas, A. J. J. Org. Chem. 2006, 71, 7087-7090;-   Gamez, P.; Arends, I. W. C. E.; Sheldon, R. A.; Reedijk, J. Adv.    Synth. Catal. 2004, 346, 805-811;-   Gamez, P.; Arends, I. W. C. E.; Reedijk, J.; Sheldon, R. A. Chem.    Commun. 2003, 2414-2415;-   Chaudhuri, P.; Hess, M.; Florke, U.; Wieghardt, K. Angew. Chem. Int.    Ed. 1998, 37, 2217-2220;-   Marko, I. E.; Giles, P. R.; Tsukazaki, M.; Brown, S. M.; Urch, C. J.    Science 1996, 274, 2044-2046;-   Zahmakiran, M.; Akbayrak, S.; Kodaira, T.; Ozkar, S. Dalton Trans.    2010, 39, 7521-7527;-   Bailie, D. S.; Clendenning, G. M. A.; McNamee, L.; Muldoon, M. J.    Chem. Commun. 2010, 46, 7238-7240;-   Conley, N. R.; Labios, L. A.; Pearson, D. M.; McCrory, C. C. L.;    Waymouth, R. M. Organometallics 2007, 26, 5447-5453;-   Guan, B.; Xing, D.; Cai, G.; Wan, X.; Yu, N.; Fang, Z.; Yang, L.;    Shi, Z. J. Am. Chem. Soc. 2005, 127, 18004-18005;-   Iwasawa, T.; Tokunaga, M.; Obora, Y.; Tsuji, Y. J. Am. Chem. Soc.    2004, 126, 6554-6555;-   Korovchenko, P.; Donze, C.; Gallezot, P.; Besson, M. Catal. Today    2007, 121, 13-21;-   Hara, T.; Ishikawa, M.; Sawada, J.; Ichikuni, N.; Shimazu, S. Green    Chem. 2009, 11, 2034-2040;-   Maeda, Y.; Kakiuchi, N.; Matsumura, S.; Nishimura, T.; Kawamura, T.;    Uemura, S. J. Org. Chem. 2002, 67, 6718-6724;-   Maeda, Y.; Kakiuchi, N.; Matsumura, S.; Nishimura, T.; Uemura, S.    Tetrahedron Lett. 2001, 42, 8877-8879;-   Jiang, N.; Ragauskas, A. J. Tetrahedron Lett. 2007, 48, 273-276; (b)    Jiang, N.;-   Ragauskas, A. J. J. Org. Chem. 2007, 72, 7030-7033;-   Radosevich, A. T.; Musich, C.; Toste, F. D. J. Am. Chem. Soc. 2005,    127, 1090-1091;-   Pawar, V. D.; Bettigeri, S.; Weng, S. S.; Kao, J. Q.; Chen, C. T. J.    Am. Chem. Soc. 2006, 128, 6308-6309;-   Weng, S. S.; Shen, M. W.; Kao, J. Q.; Munot, Y. S.; Chen, C. T.    Proc. Nat. Acad. Sci. 2006, 103, 3522-3527;-   Ohde, C.; Limberg, C. Chem. Eur. J. 2010, 16, 6892-6899;-   Hanson, S. K.; Baker, R. T.; Gordon, J. C.; Scott, B. L.; Silks, L.    A.; Thorn, D. L. J. Am. Chem. Soc. 2010, 132, 17804-17816;-   Thorn, D. L.; Harlow, R. L.; Herron, N. Inorg. Chem. 1996, 35,    547-548;-   Nica, S.; Pohlmann, A.; Plass, W. Eur. J. Inorg. Chem. 2005,    2032-2036;-   Caravan, P.; Gelmini, L.; Glover, N.; Herring, F. G.; Li, H.;    McNeill, J. H.; Rettig, S. J.; Setyawati, I. A.; Shuter, E.; Sun,    Y.; Tracey, A. S.; Yuen, V. G.; Orvig, C. J. Am. Chem. Soc. 1995,    117, 12759-12770;-   Sun, Y.; James, B. R.; Rettig, S. J.; Orvig, C. Inorg. Chem. 1996,    35, 1667-1673.-   Scheidt, W. R. Inorg. Chem. 1973, 12, 1758-1761;-   Giacomelli, A.; Floriani, C.; Duarte, A. O. D. S.; Chiesi-Villa, A.;    Guastini, C. Inorg. Chem. 1982, 21, 3310-3316; (b) Pasquali, M.;    Landi, A.; Floriani, C. Inorg. Chem. 1979, 18, 2397-2400;-   Riechel, T. L.; Sawyer, D. T. Inorg. Chem. 1975, 14, 1869-1875; (b)    Amos, L. W.;-   Sawyer, D. T. Inorg. Chem. 1974, 13, 78-83;-   Thorn, D. L.; Harlow, R. L.; Herron, N. Inorg. Chem. 1996, 35,    547-548;-   Hanson, S. K.; Baker, R. T.; Gordon, J. C.; Scott, B. L.; Silks, L.    A.; Thorn, D. L. J. Am. Chem. Soc. 2010, 132, 17804-17816;-   Giacomelli, A.; Floriani, C.; Duarte, A. O. D. S.; Chiesi-Villa, A.;    Guastini, C. Inorg. Chem. 1982, 21, 3310-3316;-   Nica, S.; Buchholz, A.; Rudoph, M.; Schweitzer, A.; Wachtler, M.;    Breitzke, H.; Buntkowsky, G.; Plass, W. Eur. J. Inorg. Chem. 2008,    2350-2359;-   Caravan, P.; Gelmini, L.; Glover, N.; Herring, F. G.; Li, H.;    McNeill, J. H.; Rettig, S. J.; Setyawati, I. A.; Shuter, E.; Sun,    Y.; Tracey, A. S.; Yuen, V. G.; Orvig, C. J. Am. Chem. Soc. 1995,    117, 12759-12770;-   Scheidt, W. R. Inorg. Chem. 1973, 12, 1758-1761; and-   Pasquali, M.; Landi, A.; Floriani, C. Inorg. Chem. 1979, 18,    2397-2400.

The invention is illustrated by the following examples which are notintended to be limiting in nature.

A. Experimental Procedures

General Considerations.

Unless specified otherwise, all vanadium complexes were prepared under adry argon atmosphere using standard glove-box and Schlenk techniques.CDCl₃, 1,2-dichloroethane-d₄, CD₂Cl₂, pyridine-d₅, and DMSO-d₆ werepurchased from Cambridge Isotope Laboratories, and CD₂Cl₂ was dried overCaH₂. Anhydrous grade acetonitrile, CH₂Cl₂, THF, 1,2-dichloroethane, anddiethyl ether were obtained from Fisher Scientific and used as received.¹H, ¹³C, and ⁵¹V NMR spectra were obtained at room temperature on aBruker AV400 MHz spectrometer, with chemical shifts (δ) referenced tothe residual solvent signal or referenced externally to V^(V)(O)(Cl)₃ (0ppm). IR spectra were obtained on a Varian 1000 FT-IR Scimitar Seriesinstrument. GC-MS analysis was obtained using a Hewlett Packard 6890 GCsystem equipped with a Hewlett Packard 5973 mass selective detector.Complexes (dipic)V^(V)(O)(O^(i)Pr) (3) (Thorn, D. L.; Harlow, R. L.;Herron, N. Inorg. Chem. 1996, 35, 547-548), (HQC)V^(V)(O)(O^(i)Pr) (4)(Hanson, S. K.; Baker, R. T.; Gordon, J. C.; Scott, B. L.; Silks, L. A.;Thorn, D. L. J. Am. Chem. Soc. 2010, 132, 17804-17816),(SAL)V^(V)(O)(O^(i)Pr)(5) (Thorn, D. L.; Harlow, R. L.; Herron, N.Inorg. Chem. 1996, 35, 547-548), [(HQ)₂V^(V)(O)]₂μ-O (12) (Giacomelli,A.; Floriani, C.; Duarte, A. O. D. S.; Chiesi-Villa, A.; Guastini, C.Inorg. Chem. 1982, 21, 3310-3316), and4-hydroxy-N′-salicylidene-butanohydrazine (H₂SALhyhb) (Nica, S.;Buchholz, A.; Rudoph, M.; Schweitzer, A.; Wachtler, M.; Breitzke, H.;Buntkowsky, G.; Plass, W. Eur. J. Inorg. Chem. 2008, 2350-2359) wereprepared using published procedures. Elemental Analyses were performedby Atlantic Microlab in Norcross, Ga. High resolution mass spectra(HRMS) were obtained by the Laboratory for Biology Mass Spectrometry atTexas A&M University in College Station, Tex.

Synthesis of (SALhyhb)V^(V)(O)(O^(i)Pr) (6)

The ligand 4-hydroxy-N′-salicylidene-butanohydrazine (H₂SALhyhb) (470mg, 2.12 mmol) was suspended in isopropanol (5 mL). V^(V)(O)(O^(i)PR)₃(522 mg, 2.14 mmol) was added, yielding a dark red solution. Within 5minutes, a red-brown precipitate began to form. Diethylether (10 mL) wasadded, and the suspension cooled to −20° C. overnight. The supernatantwas decanted, and the red-brown solid washed with diethyl ether (10 mL)and dried under vacuum. Yield: 641 mg (87%). ¹H NMR (400 MHz, CD₃OD): δ8.59 (s, 1H, C═NH), 7.59 (d, 1H, J=7.6 Hz, SAL), 7.53 (t, 1H, J=7.6 Hz,SAL), 7.01 (t, 1H, J=7.2 Hz, SAL), 6.94 (d, 1H, J=8.4 Hz, SAL), 3.95 (h,1H, J=6.0 Hz, isopropanol), 3.69 (t, 2H, J=6.8 Hz, CH₂OH), 2.54 (t, 2H,J=7.2 Hz, N—CH₂), 1.98 (quintet, 2H, J=6.8 Hz, —CH₂), 1.17 (d, 6H, J=6.0Hz, isopropanol). ¹³C{¹H} NMR (100 MHz, CD₃OD): 179.9, 165.3, 153.4,135.5, 133.8, 121.6, 121.5, 117.9, 64.9, 62.6, 30.6, 29.1, 25.4. ⁵¹V NMR(105 MHz, CD₃OD): −549 (s). IR (CH₂Cl₂): ν_(C=N)=1613 cm⁻¹, 1558 cm⁻¹,ν_(V=O)=948 cm⁻¹. Anal. Calcd for C₁₄H₁₉N₂O₅V: C, 48.56; H, 5.53; N,8.09. Found: C, 48.69; H, 5.48; N, 7.99.

Synthesis of (malt)₂V^(V)(O)(O^(i)Pr) (7)

Complex 7 has been reported previously (Caravan, P.; Gelmini, L.;Glover, N.; Herring, F. G.; Li, H.; McNeill, J. H.; Rettig, S. J.;Setyawati, I. A.; Shuter, E.; Sun, Y.; Tracey, A. S.; Yuen, V. G.;Orvig, C. J. Am. Chem. Soc. 1995, 117, 12759-12770). Maltol (1.199 g,9.516 mmol) was suspended in CH₃CN (10 mL). V^(V)(O)(O^(i)Pr)₃ (1.161 g,4.758 mmol) was added, yielding a dark red reaction mixture, which wasstirred at room temperature 5 minutes. Upon cooling the mixture to −20°C. overnight, dark red needles formed. The supernatant was decanted, andthe crystals washed with diethyl ether (2×3 mL) and dried under vacuum.Yield: 1.766 g (98%). ¹H NMR (400 MHz, CD₂Cl₂): δ 7.85 (br s, 2H, malt),6.45 (br s, 2H, malt), 6.30 (h, 1H, J=6.0 Hz, V—OCH), 2.47 (s, 6H,malt), 1.42 (br s, 6H, V-isopropoxide). ¹³C{¹H} NMR (100 MHz, CD₂Cl₂):174.8 (br), 155.5, 150.6 (br), 110.9 (br), 92.2, 24.8, 14.9. ⁵¹V NMR(105 MHz, CD₂Cl₂): −433 (s). IR (thin film): ν_(V=O)=967 cm⁻¹. ¹H NMRdata in CDCl₃ matched those reported for 7 (Caravan, P.; Gelmini, L.;Glover, N.; Herring, F. G.; Li, H.; McNeill, J. H.; Rettig, S. J.;Setyawati, I. A.; Shuter, E.; Sun, Y.; Tracey, A. S.; Yuen, V. G.;Orvig, C. J. Am. Chem. Soc. 1995, 117, 12759-12770). Anal. Calcd forC₁₅H₁₇O₈V: C, 47.89; H, 4.55. Found: C, 48.06; H, 4.48.

Synthesis of (HQ)₂V^(V)(O)(O^(i)Pr) (8)

Complex 8 has been reported previously (Giacomelli, A.; Floriani, C.;Duarte, A. O. D. S.; Chiesi-Villa, A.; Guastini, C. Inorg. Chem. 1982,21, 3310-3316 and Scheidt, W. R. Inorg. Chem. 1973, 12, 1758-1761).Under air in a 20 mL vial, V^(IV)(O)(acac)₂ (182 mg, 0.687 mmol) and8-hydroxyquinoline (199 mg, 1.37 mmol) were suspended in isopropanol (10mL). The suspension was stirred for 24 hours under air, resulting in adark red-purple suspension. The dark red solid was collected on a fritunder air, washed with isopropanol (2×1 mL), and allowed to drycompletely in the air. Yield: 247 mg (87%). ¹H NMR (400 MHz, CD₂Cl₂): δ8.56 (br s, 1H, HQ), 8.41 (br s, 1H, HQ), 8.13 (d, 1H, J=8.0 Hz, HQ),8.05 (d, 1H, J=8.0 Hz, HQ), 7.58-7.53 (m, 2H, HQ), 7.24-7.13 (m, 6H,HQ), 6.25 (h, 1H, J=6.0, V—OCH), 1.44 (d, 3H, J=6.4 Hz, V-isopropoxide),1.40 (d, 3H, J=6.0 Hz, V-isopropoxide). ¹³C{¹H} NMR (100 MHz, CD₂Cl₂):164.9, 163.8, 146.3, 145.9, 141.7, 140.0, 138.7, 137.7, 130.4, 129.8,129.4, 122.6, 122.4, 117.6, 115.2, 111.7, 110.4, 91.2, 25.3, 24.9. ⁵¹VNMR (105 MHz, CD₂Cl₂): −492 (s). IR (thin film): ν_(V=O)=957 cm⁻¹. Anal.Calcd for C₂₁H₁₉N₂O₄V: C, 60.88; H, 4.62; N, 6.76. Found: C, 60.00; H,4.51; N, 6.56.

Alternate Synthesis of 8.

In a 20 mL vial, V^(V)(O)(O^(i)Pr)₃ (1.027 g, 4.209 mmol) was added to asuspension of 8-hydroxyquinoline (1.222 g, 8.428 mmol) in CH₃CN (15 mL).The mixture was stirred at room temperature for 4 hours, and then theresulting dark red solid collected on a frit, washed with diethyl ether(3×3 mL), and dried under vacuum. Yield: 1.585 g (91%).

Synthesis of (HQ)₂V^(V)(O)(OC₆H₄OCH₃) (9)

Complex (HQ)₂V^(V)(O)(O^(i)Pr)(8) (95.6 mg, 0.231 mmol) and4-methoxybenzylalcohol (440 mg, 3.19 mmol) were suspended in CH₃CN (5mL). The mixture was allowed to stand at room temperature for 4 days,during which time dark red crystals formed. The supernatant wasdecanted, and the crystals washed with diethyl ether (2×4 mL) and driedunder vacuum. Yield: 109 mg (96%). ¹H NMR (400 MHz, CD₂Cl₂): δ 8.58 (brs, 1H, HQ), 8.41 (br s, 1H, HQ), 8.14 (d, 1H, J=8.0 Hz, HQ), 8.05 (d,1H, J=7.2 Hz, HQ), 7.59-7.52 (m, 2H, HQ), 7.29 (d, 2H, J=8.4 Hz, aryl),7.28-7.12 (m, 6H, HQ), 6.80 (d, 2H, J=8.4 Hz, aryl), 6.72 (d, 1H,J=12.8, V—OCH), 6.57 (d, 1H, J=12.8 Hz, V—OCH), 3.76 (s, 3H, OCH₃).¹³C{¹H} NMR (100 MHz, CD₂Cl₂): 163.9, 162.6, 158.8, 145.6, 145.2, 140.8,139.0, 138.0, 136.9, 132.9, 129.6, 129.5, 128.8, 128.4, 128.3, 121.7,121.5, 117.2, 114.4, 113.4, 113.1, 110.8, 109.5, 89.2, 54.8. ⁵¹V NMR(105 MHz, CD₂Cl₂): −473 (s). IR (thin film): ν_(V=O)=959 cm⁻¹. Anal.Calcd for C₂₆H₂₁N₂O₅V: C, 63.42; H, 4.30; N, 5.69. Found: C, 62.84; H,4.33; N, 5.55. HRMS (EI): m/z calcd for C₂₆H₂₂N₂O₅V [M+H]⁺: 473.1079.found: 473.1065.

Reaction of 9 with NEt₃ Under Argon.

In a resealable Teflon-capped NMR tube, complex 9 (5.2 mg, 0.011 mmol)was dissolved in CD₂Cl₂ (0.6 mL) containing diethyl ether (0.023 M) asan internal standard. An initial ¹H NMR spectrum was recorded, and thenNEt₃ (3.0 μL, 0.022 mmol) was added. After 2 h at room temperature,integration of the ¹H NMR spectrum revealed complete consumption of 9,and formation of 4-methoxybenzaldehyde (0.5 equiv, 100%) and4-methoxybenzylalcohol (0.5 equiv, 100%). Carrying out the reaction on alarger scale using 9 (28.5 mg, 0.0579 mmol) and NEt₃ (16 μL, 0.12 mmol)in CH₂Cl₂ (1.5 mL), allowed for isolation of the vanadium(IV) product asa yellow-brown precipitate (Yield: 19.5 mg, 94%). The IR spectrum of theprecipitate was consistent with (HQ)₂V^(IV)(O) (10), matching that of anauthentic sample prepared as described below. When a similar experimentwas carried out with complex 9 dissolved in CD₂Cl₂ and no NEt₃ wasadded, less than 5% of the complex reacted after 16 h at roomtemperature.

Reaction of 9 with NEt₃ Under Air.

In a resealable Teflon-capped NMR tube, complex 9 (3.6 mg, 7.3 μmol) wasdissolved in CD₂Cl₂ (0.6 mL) containing CH₃CN (0.026 M) as an internalstandard. An initial spectrum was recorded. The tube was opened to air,and NEt₃ (2.0 μL, 0.014 mmol) was added. After 22 hours at roomtemperature, examination of the ¹H NMR spectrum revealed completeconsumption of the starting material and quantitative conversion to(HQ)₂V^(V)(O)₂HNEt₃ (11) and 4-methoxybenzaldehyde. The identity of 11was verified by independent synthesis as described below.

Synthesis of (HQ)₂V^(IV)(O) (10)

Complex 10 has been reported previously, and was prepared according to amodified version of a published procedure (Pasquali, M.; Landi, A.;Floriani, C. Inorg. Chem. 1979, 18, 2397-2400). In a vial,V^(IV)(O)(acac)₂ (155 mg, 0.583 mmol) and 8-hydroxyquinoline (174 mg,1.20 mmol) were suspended in acetone. The reaction mixture was stirredat room temperature overnight, affording a yellow suspension. The yellowsolid was collected on a frit, washed with diethyl ether (1×1 mL) anddried under vacuum. Yield: 198 mg (96%). The IR spectrum of the productmatched reported data for 10 (Pasquali, M.; Landi, A.; Floriani, C.Inorg. Chem. 1979, 18, 2397-2400).

Synthesis of (HQ)₂V^(V)(O)₂HNEt₃ (11)

Under air, the μ-oxo complex [(HQ)₂V^(V)(O)]₂μ-O (12) (108 mg, 0.147mmol) was suspended in CH₂Cl₂ (8 mL). Water (26.5 μL, 1.47 mmol) andNEt₃ (205 μL, 1.47 mmol) were added, and the mixture stirred overnightat room temperature, during which time the reaction mixture changed froma gray suspension to a yellow solution. The solvent was removed undervacuum, leaving a yellow-tan solid. The solid was washed with diethylether (1×4 mL) and dried under vacuum. Yield: 107 mg (76%). The productwas somewhat unstable in the absence of NEt₃; a similar loss of aminewas reported for the n-butylammonium analogue (Giacomelli, A.; Floriani,C.; Duarte, A. O. D. S.; Chiesi-Villa, A.; Guastini, C. Inorg. Chem.1982, 21, 3310-3316). ¹H and ⁵¹V NMR spectra were recorded in thepresence of added NEt₃ (2 equiv). ¹H NMR (400 MHz, CD₂Cl₂): δ 8.44 (d,2H, J=3.6 Hz, HQ), 7.99 (d, 2H, J=8.0 Hz, HQ), 7.45 (t, 2H, J=8.0 Hz,HQ), 7.12 (dd, 2H, J=8.0 Hz, J=3.6 Hz, HQ), 7.02 (dd, 2H, J=7.6 Hz,J=2.8 Hz, HQ), 2.70 (q, 24H, J=6.8 Hz, NEt₃), 1.09 (t, 36H, J=6.8 Hz,NEt₃). ¹³C{¹H} NMR (100 MHz, CD₂Cl₂): 165.7, 144.5, 141.6, 136.8, 130.4,129.7, 121.9, 113.0, 111.6, 46.9, 12.1. ⁵¹V NMR (105 MHz, CD₂Cl₂): −526(s). IR (thin film): ν_(V=O)=853 cm⁻¹, 908 cm⁻¹. Anal. Calcd forC₂₄H₂₈N₃O₄V: C, 60.89; H, 5.96; N, 8.88. Found: C, 60.07; H, 5.98; N,8.67. HRMS (EI): m/z calcd for C₁₈H₁₂N₂O₄V [M]⁻: 370.0269. found:370.0256.

General Procedure for the Catalytic Oxidation.

In a 50 mL roundbottom flask, the substrate (1.0 mmol) was combined withcomplex 8 (8.3 mg, 0.020 mmol) and NEt₃ (14 μL, 0.10 mmol). The mixturewas dissolved in 1,2-dichloroethane (2 mL) under air, and the flaskequipped with a stir bar and an air condenser. The flask was heated withstirring in an oil bath at 60° C. for 24 h under air. To isolate theproduct, the solvent was removed under vacuum, and the dark residue wasextracted with ethyl acetate/hexanes (3:7), filtered through a plug ofsilica gel, and the solvent removed under vacuum.

Unless noted otherwise, the general procedure was followed to isolatethe products below:

benzaldehyde (92% yield). ¹H NMR (400 MHz, CDCl₃): δ 10.03 (s, 1H), 7.90(d, 2H, J=7.6 Hz), 7.65 (t, 1H, J=7.6 Hz), 7.55 (t, 2H, J=7.6 Hz).¹³C{¹H} NMR (100 MHz, CDCl₃): δ 192.6, 136.6, 134.7, 130.0, 129.2.4-methoxybenzaldehyde (96% yield). ¹H NMR (400 MHz, CDCl₃): δ 9.90 (s,1H), 7.85 (d, 2H, J=8.8 Hz), 7.02 (d, 2H, J=8.8 Hz), 3.90 (s, 3H).¹³C{¹H} NMR (100 MHz, CDCl₃): δ 191.1, 164.8, 132.2, 130.1, 114.5, 55.8.4-nitrobenzaldehyde (96% yield). ¹H NMR (400 MHz, CDCl₃): δ 10.16 (s,1H), 8.39 (d, 2H, J=8.0 Hz), 8.08 (d, 2H, J=8.0 Hz). ¹³C{¹H} NMR (100MHz, CDCl₃): δ 190.5, 151.3, 140.2, 130.7, 124.5.benzophenone (93% yield). The reaction was heated at 60° C. for 72 h. ¹HNMR (400 MHz, CDCl₃): δ 7.82 (d, 4H, J=8.0 Hz), 7.60 (t, 2H, J=8.0 Hz),7.50 (t, 4H, J=8.0 Hz). ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 197.0, 137.8,132.6, 130.3, 128.5.acetophenone (95% yield). The reaction was heated at 80° C. for 24 husing 1 equiv of NEt₃. ¹H NMR (400 MHz, CDCl₃): δ 7.96 (d, 2H, J=7.2Hz), 7.56 (t, 1H, J=7.2 Hz), 7.46 (t, 2H, J=8.0 Hz), 2.61 (t, 3H).¹³C{¹H} NMR (100 MHz, CDCl₃): δ 198.3, 137.3, 133.3, 128.7, 128.5, 26.8.cyclopropylphenylketone (90% yield). The reaction was heated at 80° C.for 48 h. ¹H NMR (400 MHz, CDCl₃): δ 8.03 (d, 2H, J=8.0 Hz), 7.58 (t,1H, J=7.6 Hz), 7.49 (t, 2H, J=7.6 Hz), 2.69 (m, 1H), 1.26 (m, 2H), 1.05(m, 2H). ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 200.9, 138.2, 132.9, 128.7,128.2, 17.3, 11.8.cinnamyl aldehyde (98% yield). ¹H NMR (400 MHz, CDCl₃): δ 9.72 (d, 1H,J=7.2 Hz), 7.60-7.57 (m, 2H), 7.49 (d, 1H, J=16.0 Hz), 7.46-7.44 (m,3H), 6.74 (dd, 1H, J=16.0 Hz, J=7.6 Hz). ¹³C{¹H} NMR (100 MHz, CDCl₃): δ194.0, 153.0, 134.2, 131.5, 129.3, 128.8, 128.7.3-methyl-2-cyclohexen-1-one (96% yield). The reaction was heated at 80°C. ¹H NMR (400 MHz, CDCl₃): 5.88 (m, 1H), 2.34 (t, 2H, J=6.8 Hz), 2.28(t, 2H, J=6.4 Hz), 1.99 (p, 2H, J=6.4 Hz), 1.96 (s, 3H). ¹³C{¹H} NMR(100 MHz, CDCl₃): δ 200.0, 162.9, 126.9, 37.2, 31.1, 24.6, 22.7.pyridine-2-carbaldehyde (96% yield). The reaction was heated at 80° C.¹H NMR (400 MHz, CDCl₃): δ 10.08 (s, 1H), 8.79 (d, 1H, J=4.8 Hz), 7.97(d, 2H, J=7.6 Hz), 7.88 (t, 1H, J=7.6 Hz), 7.54-7.51 (m, 1H). ¹³C{¹H}NMR (100 MHz, CDCl₃): δ 193.6, 153.0, 150.4, 137.3, 128.1, 121.9.2,5-diformylfuran (93% yield). ¹H NMR (400 MHz, CDCl₃): δ 9.87 (s, 2H),7.34 (s, 2H). ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 179.4, 154.4, 119.4.2-allyloxybenzaldehyde (95% yield). ¹H NMR (400 MHz, CDCl₃): δ 10.54 (s,1H), 7.84 (dd, 1H, J=7.6 Hz, J=1.6 Hz, aryl), 7.55 (dd, 1H, J=8.4 Hz,J=1.6 Hz, aryl), 7.03 (t, 1H, J=7.6 Hz, aryl), 6.98 (d, 1H, J=8.4 Hz,aryl), 6.07 (m, 1H, OCH₂CH═CH₂), 5.46 (d, 1H, J=16.8 Hz, OCH₂CH═CHH),5.34 (d, 1H, J=10.8 Hz, OCH₂CH═CHH), 4.66 (d, 2H, J=5.2 Hz, OCH₂CH═CH₂).¹³C{¹H} NMR (100 MHz, CDCl₃): δ 189.9, 161.1, 136.0, 132.5, 128.6,125.2, 121.0, 118.2, 113.0, 69.3.4-phenyl-3-butyn-2-one (96% yield). The reaction was heated at 80° C. ¹HNMR (400 MHz, CDCl₃): δ 7.58-7.57 (m, 2H), 7.47-7.43 (m, 1H), 7.40-7.36(m, 2H), 2.45 (s, 3H). ¹³C NMR (100 MHz, CDCl₃): δ 184.8, 133.2, 130.9,128.8, 120.0, 90.5, 88.4, 32.9.

General Procedure for Testing Catalysts.

In a 50 mL roundbottom flask, 4-methoxybenzylalcohol (70 mg, 0.50 mmol),the appropriate vanadium complex (0.01 mmol), NEt₃ (7 μL, 0.05 mmol) anda 1,3,5-tri-tert-butylbenzene internal standard (ca. 10 mg, 0.04 mmol)were dissolved in 1,2-dichloroethane (1 mL) under air. The flask wasequipped with a stir bar and an air condenser. The flask was heated withstirring under air for 24 h at 60° C., then cooled to room temperatureand the solvent removed under vacuum. The residue was dissolved in CDCl₃(0.6 mL), and the yield of 4-methoxybenzaldehyde determined byintegration of the ¹H NMR spectrum against the internal standard.

General Procedure for Testing Solvents.

In a 50 mL roundbottom flask, 4-methoxybenzylalcohol (70 mg, 0.50 mmol),complex 8 (4.2 mg, 0.010 mmol), NEt₃ (7 μL, 0.05 mmol), and a1,3,5-tri-tert-butylbenzene internal standard (ca. 5 mg, 0.02 mmol) weredissolved in the appropriate solvent (1 mL). The flask was equipped witha stir bar and an air condenser, and the mixture was heated at 60° C.for 24 hours under air with stirring. The reaction mixture was cooled toroom temperature and the solvent removed under vacuum. The residue wasdissolved in CDCl₃ and the yield of 4-methoxybenzaldehyde determined byintegration of the ¹H NMR spectrum against the internal standard. Todetermine the reaction yield in pyridine and DMSO solvents, analogouscatalytic reactions were carried out in pyridine-d₅ and DMSO-d₆ solventand the yield determined by integration of the ¹H NMR spectrum.

General Procedure for Solvent-Free Catalytic Oxidation.

In a 25 mL roundbottom flask, the substrate (2.0 mmol) was combined withcomplex 8 (17 mg, 0.040 mmol) and NEt₃ (28 μL, 0.20 mmol). The flask wasequipped with an air condenser and a stir bar and the reaction mixturewas heated at 100° C. for 24 h. After cooling to room temperature, theresidue was extracted with ethyl acetate/hexanes (3:7), filtered througha plug of silica gel, and the solvent removed under vacuum. Thisprocedure afforded high yields of benzaldehyde (95%),4-methoxybenzaldehyde (96%), acetophenone (92%), benzophenone (99%),cyclopropylphenylketone (89%), and isopropylphenylketone (95%). Althoughbenzaldehyde and 4-methoxybenzaldehyde were isolated selectivelyimmediately following the reaction, further oxidation to thecorresponding benzoic acid was observed when the isolated product stoodfor several days at room temperature. This solvent-free procedure wasnot generally extended to the allylic and propargylic alcohols, as lowerselectivity was observed in the oxidation of 3-methyl-2-cyclohexen-1-ol,which afforded 3-methyl-2-cyclohexen-1-one in 74% yield. Lowerselectivity was also observed when cinnamyl alcohol and4-phenyl-3-butyn-2-ol were oxidized following this procedure.

General Procedure for Testing Additives.

In a 50 mL roundbottom flask, 4-methoxybenzylalcohol (70 mg, 0.50 mmol),complex 8 (4.2 mg, 0.010 mmol), the appropriate additive (0.05 mmol),and a 1,3,5-tri-tert-butylbenzene internal standard (ca. 6 mg, 0.02mmol) were dissolved in 1,2-dichloroethane (1 mL). The flask wasequipped with a stir bar and an air condenser and the mixture was heatedat 60° C. for 24 hours under air with stirring. The reaction mixture wascooled to room temperature and the solvent removed under vacuum. Theresidue was dissolved in CDCl₃ and the yield of 4-methoxybenzaldehydedetermined by integration of the ¹H NMR spectrum against the internalstandard.

Catalytic Oxidation of 2-Allyloxybenzyl Alcohol (10 Mmol Scale).

In a 500 mL roundbottom flask, 2-allyloxybenzyl alcohol (1.640 g, 10.00mmol), complex 8 (0.0823 g, 0.199 mmol), and triethylamine (140 μL, 1.01mmol) were dissolved in 1,2-dichloroethane (20 mL). The flask wasequipped with a stir bar and an air condenser and heated at 60° C. for24 h. At this time, TLC of the reaction mixture indicated that thereaction was not yet complete. The flask was heated for an additional 14h under air, and then cooled to room temperature. The solvent wasremoved under vacuum, and the dark liquid eluted through silica gelusing ethyl acetate/hexanes (3:7). Yield: 1.517 g (94%). A minor productidentified as 2-allyloxycinnamyl aldehyde was also detected by ¹H NMR inapproximately 2-4% yield; this product was isolated for characterizationby prep-scale TLC chromatography on silica gel using 9:1 hexanes:ethylacetate. ¹H NMR for 2-allyloxycinnamyl aldehyde (400 MHz, CDCl₃) δ 9.71(d, 1H, J=8.0 Hz, HC═O), 7.89 (d, 1H, J=16.4 Hz, aryl-CH═CH), 7.58 (dd,1H, J=7.6, 1.6 Hz, aryl), 7.40 (dt, 1H, J=7.6, 1.6 Hz, aryl), 7.02 (t,1H, J=7.6 Hz, aryl), 6.95 (d, 1H, J=8.0 Hz, aryl), 6.81 (dd, 1H, J=16.4,8.0 Hz, aryl-CH═CHCHO), 6.11 (m, 1H, OCH₂CH═CH₂), 5.45 (d, 1H, J=17.2Hz, OCH₂CH═CHH), 5.35 (d, 1H, J=10.4 Hz, OCH₂CH═CHH), 4.66 (d, 2H, J=5.6Hz, OCH₂CH═CH₂). ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 194.8, 157.5, 148.3,132.9, 132.8, 129.3, 129.1, 123.5, 121.3, 118.4, 112.8, 69.5. MS (EI)m/z: 188 (M⁺), 147, 131, 118, 103, 91.

Catalytic Oxidation of 3-phenyl-2-propyn-1-ol.

Complex 8 (4.1 mg, 0.010 mmol), NEt₃ (7 μL, 0.05 mmol),3-phenyl-2-propyn-1-ol (69 mg, 0.52 mmol), and a1,3,5-tri-tert-butylbenzene internal standard (13 mg, 0.051 mmol) weredissolved in 1,2-dichloroethane-d₄ (1 mL). An initial ¹H NMR spectrumwas recorded, and then the reaction mixture heated at 60° C. for 24 hunder air with stirring in a 100 mL roundbottom flask equipped with anair condenser. The reaction mixture was cooled to room temperature, andthen the mixture transferred to an NMR tube. Examination of the ¹Hspectrum revealed the formation of 3-phenyl-2-propyn-1-al in 80% yield.¹H NMR (400 MHz, 1,2-dichloroethane-d₄) δ 9.42 (s, 1H), 7.63 (d, 2H,J=7.6 Hz), 7.51 (t, 1H, J=7.6 Hz), 7.43 (t, 2H, J=7.6 Hz). ¹³C{¹H} NMR(100 MHz, 1,2-dichloroethane-d₄): δ 176.8, 133.4, 131.5, 129.0, 119.6,94.4, 88.6.

Catalytic Oxidation of 2-decyn-1-ol.

Complex 8 (1.4 mg, 0.0034 mmol), NEt₃ (2.4 μL, 0.018 mmol), 2-decyn-1-ol(27 mg, 0.18 mmol) and a 1,3,5-tri-tert-butylbenzene internal standard(9.5 mg, 0.039 mmol) were dissolved in 1,2-dichloroethane-d₄ (0.7 mL).An initial ¹H NMR spectrum was recorded, and then the mixture heated at60° C. for 24 h with stirring in a 50 mL roundbottom flask equipped withan air condenser. The mixture was cooled to room temperature andtransferred to an NMR tube. ¹H and ¹³C NMR spectra indicated theformation of 2-decyn-1-al in 60% yield. ¹H NMR (400 MHz,1,2-dichloroethane-d₄) δ 9.16 (s, 1H), 2.42 (t, 2H, J=7.2 Hz), 1.59 (p,2H, J=7.2 Hz), 1.43-1.30 (m, 8H), 0.90 (t, 3H, J=7.2 Hz). ¹³C{¹H} NMR(100 MHz, 1,2-dichloroethane-d₄): δ 177.1, 99.0, 81.9, 31.9, 29.0, 28.9,27.9, 22.8, 19.2, 14.1.

Catalytic Oxidation of 1-phenyl-2-propyn-1-ol.

Complex 8 (2.9 mg, 0.0070 mmol), NEt₃ (4.8 μL, 0.035 mmol),1-phenyl-2-propyn-1-ol (46 mg, 0.35 mmol), and a1,3,5-tri-tert-butylbenzene internal standard (14 mg, 0.056 mmol) weredissolved in 1,2-dichloroethane-d₄. An initial ¹H NMR spectrum wasrecorded, and then the reaction mixture heated at 60° C. for 24 h withstirring in a 50 mL roundbottom flask equipped with an air condenser.The mixture was cooled to room temperature and transferred to an NMRtube. ¹H and ¹³C NMR spectra revealed complete consumption of thestarting material and the formation of 1-phenyl-2-propyn-1-one in 38%yield. ¹H NMR (400 MHz, 1,2-dichloroethane-d₄) δ 8.39 (s, 1H), 7.87 (d,2H, J=7.6 Hz), 7.64 (t, 1H, J=7.6 Hz), 7.54 (t, 2H, J=7.6). ¹³C{¹H} NMR(100 MHz, 1,2-dichloroethane-d₄): δ 194.6, 138.3, 136.8, 134.1, 133.3,130.2, 128.8.

Effect of Flask Size on the Catalytic Oxidation of4-Methoxybenzylalcohol.

A stock solution was prepared by dissolving 4-methoxybenzylalcohol(0.277 g, 2.01 mmol), complex 8 (0.017 g, 0.040 mmol), NEt₃ (28 μL, 0.20mmol), and a 1,3,5-tri-tert-butylbenzene internal standard (0.049 g,0.20 mmol) in 1,2-dichloroethane (4 mL). The stock solution was splitbetween a 100 mL roundbottom flask (2 mL) and a 10 mL Schlenk tube (2mL). Each flask was equipped with a stir bar and an air condenser andheated at 60° C. for 4 hours with stirring. The reactions were cooled toroom temperature, the solvent removed under vacuum, and the residuedissolved in CDCl₃. The extent of conversion was determined byintegration against the internal standard; 55% conversion was observedin the wider 100 mL flask, while only 31% conversion was observed in thenarrow 10 mL tube.

Effect of Stir Rate on the Catalytic Oxidation of4-Methoxybenzylalcohol.

A stock solution was prepared by dissolving 4-methoxybenzylalcohol(0.276 g, 2.00 mmol), complex 8 (0.0166 g, 0.0401 mmol), NEt₃ (28 μL,0.20 mmol), and a 1,3,5-tri-tert-butylbenzene internal standard (0.066g, 0.27 mmol) in 1,2-dichloroethane (4 mL). To each of two 25 mLroundbottom flasks was added 2 mL of the stock solution. The flasks wereeach equipped with an air condenser and heated at 60° C. using an IKAWerke basic temperature controlled oil bath. The first flask was stirredat ˜900 rpm (setting level 8), while the second flask was stirred at˜200 rpm (setting level 2). After 4 hours of heating, the reactions werecooled to room temperature and the solvent removed under vacuum. Theresidue in each flask was dissolved in CDCl₃, and the extent ofconversion determined by integration against the internal standard. Theflask stirred at ˜900 rpm showed 43% conversion, while the flask stirredat ˜200 rpm showed only 35% conversion.

Catalytic Oxidation with Added H₂O.

Complex 8 (8.8 mg, 0.021 mmol) and NEt₃ (14 μL, 0.10 mmol) weredissolved in 1,2-dichloroethane (2 mL). The solution was added to aflask containing 4-methoxybenzyl alcohol (140 mg, 1.01 mmol), H₂O (91μL, 5.05 mmol), and a 1,3,5-tri-tert-butylbenzene internal standard(19.2 mg, 0.078 mmol). The flask was equipped with an air condenser anda stir bar and heated at 60° C. for 24 h with stirring (˜700 rpm). Thereaction mixture was cooled to room temperature, the solvent removedunder vacuum, and the extent of conversion determined by integration ofthe ¹H NMR spectrum against the internal standard. 4-Methoxybenzaldehydewas formed in >98% yield (based on the average of two runs of thistype).

Catalytic Oxidation of a Mixture of 4-Methoxybenzyl Alcohol and1-Octanol.

In a 50 mL roundbottom flask under air, 4-methoxybenzyl alcohol (68.9mg, 4.99 mmol) and complex 8 (8.3 mg, 0.020 mmol) were dissolved in1,2-dichloroethane (2 mL). 1-Octanol (79 μL, 5.0 mmol) and triethylamine(14 μL, 0.10 mmol) were added. The flask was equipped with a stir barand an air condenser, and heated at 60° C. for 24 h with stirring. Thereaction mixture was cooled to room temperature and the solvent removedunder vacuum. The product mixture was isolated by extraction of the darkresidue with a mixture of ethyl acetate and hexanes (3:7), filtrationthrough a plug of silica gel in a pipette, and removal of the solventunder vacuum. Yield: 128 mg (96% material recovery). Examination of the¹H and ¹³C NMR spectra of the products revealed a mixture of4-methoxybenzaldehyde and 1-octanol. No 1-octanal was detected.

1. A process for oxidizing an alcohol to produce a carbonyl compound,said process comprising contacting the alcohol with (i) a gaseousmixture comprising oxygen; and (ii) an amine compound; said contactingoccurring in the presence of a catalyst, said catalyst comprising twonitrogen-containing heterocycles complexed with vanadium and having theformula:

wherein: each of R¹-R¹² are independently H, alkyl, aryl, CF₃, halogen,OR¹³, SO₃R¹⁴, C(O)R¹⁵, CONR¹⁶R¹⁷ or CO₂R^(18;) each of R¹³-R¹⁸ isindependently alkyl or aryl; and Z is alkl or aryl.
 2. The method ofclaim 1, wherein Z is alkyl.
 3. The method of claim 1, wherein Z isisopropyl.
 4. The method of claim 1, wherein said amine is a trialkylamine.
 5. The method of claim 1, wherein said amine is triethylamine. 6.The method of claim 1, wherein each of R¹-R¹² is H, alkyl or aryl. 7.The method of claim 1, wherein each of R¹-R¹² is H.
 8. The method ofclaim 7, wherein Z is isopropyl.
 9. The method of claim 8, wherein saidamine is triethylamine, diisopropylethylamine,1,4-diazabicyclo[2.2.2]octane, or 2,2,6,6-tetramethylpiperidine-1-oxyl.10. The method of claim 8, wherein said amine is triethylamine.
 11. Themethod of claim 1, wherein said alcohol is of the formula

wherein R¹⁹ is selected from aryl, vinyl, and alkynyl, and wherein R²⁰is selected from H, methyl, and aryl.
 12. The method of claim 9, whereinsaid alcohol is of the formula

wherein R¹⁹ is selected from aryl, vinyl, and alkynyl, and wherein R²⁰is selected from H, methyl, and aryl.
 13. The method of claim 1, whereinsaid contacting occurs in the presence of a solvent selected from one ormore of water, 1,2-dichloroethane, ethylacetate, toluene,tetrahydrofuran, acetonitrile, dichloromethane, 1,2-dichlorobenzene and2-methyl-tetrahydrofuran.
 14. The method of claim 1, wherein saidalcohol is a benzylic alcohol, allylic alcohol, or propargylic alcohol.15. The method of claim 1, wherein said contacting occurs at atemperature in the range of from 25° C. to 150° C.
 16. The method ofclaim 15, wherein said catalyst is of the formula


17. The method of claim 1, wherein said gaseous mixture is air.